Definition: Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood. Rhabdomyosarcoma is a soft tissue tumor of striated muscle origin. It is observed mainly in children and adolescents. Rhabdomyosarcoma predominantly occurs in three regions: head and neck, genito-urinary tract and retroperitoneum, and upper and lower extremities.

Rhabdomyosarcoma is the fourth most common solid tumor and the most common soft tissue sarcoma in children. It can occur anywhere, except the brain, as it arises from totipotential mesenchymal cells.

It is an aggressive tumor with local invasion and a tendency for early recurrence if not completely excised.

It is most often seen in children between the ages of two and six years and carries the poorest prognosis when seen in children under twelve months.

The most common histologic type, embryonal rhabdomyosarcoma, offers the best prognosis. Most tumors originate in the pelvis or genitourinary tract (39% of cases) with 31% occurring in the head and neck region.

The treatment is usually chemotherapy with or without radiotherapy and subsequent surgery. The five year survival is 40%.

Differential diagnosis

While, in the past, this distinction was made largely on architectural grounds (i.e. the presence of alveolar spaces), it is nowadays recognized that cytological features are most reliable in this regard—specifically, the cells of alveolar rhabdomyosarcoma have more uniform morphology, are more consistently rounded and have larger nuclei than those of embryonal rhabdomyosarcoma.

In addition, pleomorphic rhabdomyosarcoma, which is virtually confined to adults, is diagnosed somewhat more often nowadays, largely as a result of the implementation of more sensitive and specific immunostains.

Pleomorphic rhabdomyosarcomas are among the most aggressive pleomorphic sarcomas of adulthood.